title: Housefly population density correlates with shigellosis among children in Mirzapur, Bangladesh: a time series analysis.
abstract: BACKGROUND
  Shigella infections are a public health problem in developing and transitional countries because of high transmissibility, severity of clinical disease, widespread antibiotic resistance and lack of a licensed vaccine. Whereas Shigellae are known to be transmitted primarily by direct fecal-oral contact and less commonly by contaminated food and water, the role of the housefly Musca domestica as a mechanical vector of transmission is less appreciated. We sought to assess the contribution of houseflies to Shigella-associated moderate-to-severe diarrhea (MSD) among children less than five years old in Mirzapur, Bangladesh, a site where shigellosis is hyperendemic, and to model the potential impact of a housefly control intervention.
  
  
  METHODS
  Stool samples from 843 children presenting to Kumudini Hospital during 2009-2010 with new episodes of MSD (diarrhea accompanied by dehydration, dysentery or hospitalization) were analyzed. Housefly density was measured twice weekly in six randomly selected sentinel households. Poisson time series regression was performed and autoregression-adjusted attributable fractions (AFs) were calculated using the Bruzzi method, with standard errors via jackknife procedure.
  
  
  RESULTS
  Dramatic springtime peaks in housefly density in 2009 and 2010 were followed one to two months later by peaks of Shigella-associated MSD among toddlers and pre-school children. Poisson time series regression showed that housefly density was associated with Shigella cases at three lags (six weeks) (Incidence Rate Ratio = 1.39 [95% CI: 1.23 to 1.58] for each log increase in fly count), an association that was not confounded by ambient air temperature. Autocorrelation-adjusted AF calculations showed that a housefly control intervention could have prevented approximately 37% of the Shigella cases over the study period.
  
  
  CONCLUSIONS
  Houseflies may play an important role in the seasonal transmission of Shigella in some developing country ecologies. Interventions to control houseflies should be evaluated as possible additions to the public health arsenal to diminish Shigella (and perhaps other causes of) diarrheal infection.
authors.affiliation: Center for Vaccine Development, School of Medicine, University of Maryland, Baltimore, Maryland, United States of America. tfarag@medicine.umaryland.edu
authors.forename: Tamer H
authors.initials: TH
authors.lastname: Farag
authors.forename: Abu S
authors.initials: AS
authors.lastname: Faruque
authors.forename: Yukun
authors.initials: Y
authors.lastname: Wu
authors.forename: Sumon K
authors.initials: SK
authors.lastname: Das
authors.forename: Anowar
authors.initials: A
authors.lastname: Hossain
authors.forename: Shahnawaz
authors.initials: S
authors.lastname: Ahmed
authors.forename: Dilruba
authors.initials: D
authors.lastname: Ahmed
authors.forename: Dilruba
authors.initials: D
authors.lastname: Nasrin
authors.forename: Karen L
authors.initials: KL
authors.lastname: Kotloff
authors.forename: Sandra
authors.initials: S
authors.lastname: Panchilangam
authors.forename: James P
authors.initials: JP
authors.lastname: Nataro
authors.forename: Dani
authors.initials: D
authors.lastname: Cohen
authors.forename: William C
authors.initials: WC
authors.lastname: Blackwelder
authors.forename: Myron M
authors.initials: MM
authors.lastname: Levine
mesh_terms: D000818:Animals; D001459:Bangladesh / Q000453:epidemiology; D002675:Child, Preschool; D004405:Dysentery, Bacillary / Q000453:epidemiology* / Q000635:transmission*; D019353:Endemic Diseases; D005260:Female; D006793:Houseflies / Q000254:growth & development*; D006801:Humans; D015994:Incidence; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D011156:Population Density; D012621:Seasons